Method of cleaning glass

ABSTRACT

A METHOD OF CLEANING A GLASS SURFACE BY APPLYING A MIXTURE OF AMMONIUM PERSULFATE AND SULFURIC ACID TO THE SURFACE AND THEN RINSING THE SURFACE WITH WATER. THE METHOD LEAVES THE GLASS FREE OF AGENTS WHICH COULD INTERFERE WITH SUBSEQUENT ANALYTICAL TESTS PERFORMED USING THE GLASSWARE.

United States Patent Office 3,660,294 Patented May 2, 1972 ABSTRACT OF THE DISCLOSURE A method of cleaning a glass surface by applying a mixture of ammonium persulfate and sulfuric acid to the surface and then rinsing the surface with water. The method leaves the glass free of agents which could interfere with subsequent analytical tests performed using the glassware.

BACKGROUND OF THE INVENTION This invention relates to a cleaning method and, more particularly, to a method of cleaning laboratory glassware.

The modern clinical or medical research laboratory utilizes numerous glassware items which require frequent cleaning. These items range from simple glass beakers and pipettes to the complex glass coils and flow cells incorporated in certain analytical equipment. Stains and deposits which adhere to laboratory glassware are difficult to remove, with the stains left by blood and other biological materials being particularly troublesome.

It is well known that a mixture consisting of sulfuric acid and chromic acid is a particularly effective glass cleaning solution. Chromic acid is highly toxic, but this mixture of two strong oxidizing agents is nevertheless in widespread use as it is capable of removing heavy stains which resist conventional laboratory detergents. It has been generally found, however, that cleaning solutions containing dichromates tend to interfere with subsequent analytical tests which are performed using the cleaned glassware, probably because remaining dichromate ions react with delicately balanced test reagents. The Pharmacopeia of the United States of America (th Revision) notes at page 836 that success in conducting many pharmacopeial assays depends upon the utmost cleanliness of the apparatus used. It further notes that a mixture of sulfuric acid and chromic acid is effective in removing organic matter from glass, but states that the glass must then be extensively rinsed since glass tends to adsorb chromic acid. Other glass cleaning methods suggested in Pharmacopeia have accompanying disadvantages. Alkaline cleansing agents, such as trisodium phosphate, also require prolonged rinsing whereas nitric acid generally requires heating to be an effective cleaning agent.

The extra time and trouble needed for extensive rinsing as well as the risk of subsequent altered test results are clear disadvantages of certain glass cleaning agents, and especially the toxic dichromate-containing agents. Accordingly, it is an object of the present invention to provide a method of cleaning glassware which offers the cleaning power of dichromates but without the indicated disadvantages.

SUMMARY OF THE INVENTION The present invention is directed to a method of cleaning a glass surface which comprises of the steps of applying a mixture of sulfuric acid and ammonium persulfate to the surface and then rinsing the surface with water. It has been found that glass cleaned by this method does not interfere with even the most delicate subsequent analytical tests. Furthermore, the disclosed cleaning method, which utilizes a less toxic persulfate, is as effective at removing tough stains as methods which utilize highly toxic dichromates.

Further advantages of the invention will become more apparent from the following detailed description.

DESCRIPTION OF THE PREFERRED EMBODIMENT The cleaning solution utilized in the present method is preferably prepared by dissolving ammonium persulfate in water and then adding sulfuric acid to the ammonium persulfate solution. The glass surface to be cleaned can be immersed in the cleaning solution and then briefly in a water bath. In instances where glass coils or cells are to be cleaned, the cleaning solution and then the water can be successively pumped through the coil or cell. The cleaning solution is originally colorless, but turns yellow when it begins to lose its oxidizing power as after prolonged use. When the yellow color becomes evident the cleaning solution should be discarded and replaced by a fresh supply.

EXAMPLE A solution of ammonium persulfate in water was made by adding about 23 grams of (NHQ S O to 40 milliliters of water to form a 2.5 molar solution. To this solution 1000 milliliters of 98% sulfuric acid was added. A group of glass pipettes having heavy blood stains on their inner surfaces were immersed in this cleaning mixture for a period of about one hour after which all stains appeared to have dissolved. The pipettes were then rinsed briefly in distilled water. Subsequent analytical tests performed using these pipettes were found to be unaffected by the cleaning method which had been used.

It has been ascertained that certain delicate analytical procedures, such as iron assays and enzyme determinations, which cannot be safely performed with glassware that had been cleaned with a dichromate (even after extensive rinsing), can be satisfactorily performed using glassware that was cleaned by the method of the invention. Hence, applicants method makes a significant contribution to the art in terms of providing an effective cleaning method which eliminates restricting disadvantages of presently used methods.

What is claimed is:

l. The method of cleaning a glass surface comprising the steps of applying a mixture of 98% sulfuric acid and 2.5 molar solution of ammonium persulfate in water to the surface and then rinsing the surface with water, said mixture being in the ratio of 40 milliliters of ammonium persulfate solution to 1000 milliliters of sulfuric acid.

References Cited UNITED STATES PATENTS 252-Dig. 10, 136, 186; 8-101, 111; l343, 42 

